Boom assembly

ABSTRACT

A telescopic boom broadly comprises an elongated hollow outer boom, an elongated inner boom telescopically received within the outer boom, and a guidance structure for guiding the inner boom for telescopic movement is provided. The guidance structure includes a plurality of guide rails attached to the interior corners of the outer boom, a first roller assembly attached to one end of the inner boom, a second roller assembly attached to one end of the outer boom, and a mid roller assembly positioned proximal to the second roller assembly. The first roller assembly includes a plurality of wheels mounted on axles for engaging the guide rails. The second roller assembly includes a pair of roller bars positioned on opposed sides of one end of the outer boom for guiding the inner boom during telescopic movement. The mid roller assembly includes a third roller bar that engages guide rails positioned on the inner boom.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention relate to telescopic boom devices.More particularly, embodiments of the present invention relate toassemblies for guiding the boom during telescopic movement.

2. Description of the Related Art

Telescopic boom devices are commonly used in applications requiringrapid extension and retraction of a working tool. For example,telescopic booms are commonly used in underground mining operations forworking on the ceiling or upper surface of the mine. These telescopicbooms may be provided with scaling tools which knock down loose depositsfrom the ceiling of the mine to stabilize the mine before workers areallowed to enter.

The telescopic booms often include an inner boom and a surrounding outerboom, such that the inner boom may retract and extend within the outerboom. One such implementation of the boom may include upper and lowerrollers affixed to the free end of the outer boom that engage the upperand lower exterior corners of the inner boom. In addition, there may beupper and lower rollers affixed to one end of the inner boom that engagethe upper and lower interior corners of the outer boom. During extensionof the inner boom, particularly at its greatest extent, the load at thetooling end of the boom may exert a compressive force between the upperrollers on the inner boom and the upper interior corners of the outerboom. Such a pressure on the rollers may cause them to fail, leading tofrequent equipment repair and delays in operations.

SUMMARY OF THE INVENTION

Embodiments of the present invention solve the above-mentioned problemsand provide a distinct advance in the art of telescopic boom devices.More particularly, embodiments of the invention provide an assembly thatcouples to an outer boom that reduces the pressure exerted on rollerwheels attached to an inner boom.

Various embodiments of the present invention include a roller assemblyfor use with a telescopic boom apparatus including an extensible innerboom and an outer boom, wherein the roller assembly broadly comprises ahousing, a forward stabilizer, a rear stabilizer, and a roller bar. Thehousing may couple to the outer boom and may include a first side wall,a second side wall, a forward wall, and a rear wall. The forward walland the rear wall both may include a generally rectangular opening witha recess in each corner that allows a first set of guide rails that aresecured to the outer boom to pass therethrough. The outer surfaces ofthe forward wall and the rear wall may be configured to contact edges ofan outer boom upper wall, an outer boom first side wall, and an outerboom second side wall created by a break along the length of each wall.

The forward stabilizer and the rear stabilizer both may include astabilizer upper wall, a stabilizer first side wall, and a stabilizersecond side wall. The stabilizer upper wall may be angled downward fromthe forward wall and configured to contact the outer boom upper wall.The stabilizer first side wall and the stabilizer second side wall maybe coupled to the edges of the stabilizer upper wall, angled inwardtherefrom, and configured to contact an upper portion of the first setof guide rails.

The roller bar may be coupled to the first side wall and the second sidewall, and may be configured to engage an upper portion of a second setof guide rails that are secured to the inner boom in order to relievethe pressure exerted on roller wheels attached to the inner boom whenthe inner boom is under load.

Other embodiments of the present invention include a telescopic boomapparatus broadly comprising an elongated hollow outer boom, anelongated inner boom telescopically received within the outer boom, anda guidance system.

The outer boom may include opposed proximal and distal ends and a hollowpassageway extending therebetween. The distal end generally presents across-sectional width. The inner boom is capable of axial movement inand out of the distal end of the outer boom and also may include opposedproximal and distal ends.

The guidance structure may include a first set of elongated guide rails,a plurality of roller wheels, a second set of elongated guide rails, apair of roller bars, and a roller assembly. The first set of guide railsmay be secured within the outer boom passageway and may extend parallelto the longitudinal axis of the outer boom. Each of the first set guiderails may include an arcuate track surface. The roller wheels may bespaced circumferentially about the proximal end of the inner boom. Eachof the roller wheels may include an arcuate rail engaging surface forengaging the track surfaces of the first set of guide rails duringtelescoping movement of the inner boom. The second set of guide railsmay be secured to the inner boom. The roller bars may be secured to thedistal end of the outer boom for engaging the second set of guide railsfor guiding the inner boom during axial telescoping movement in and outof the distal end of the outer boom. The roller bars may be positionedon opposed sides of the distal end of the outer boom and extend acrosssubstantially the entire cross sectional width of the distal end of theouter boom.

The roller assembly may include a housing, a forward stabilizer, a rearstabilizer, and a roller bar. The housing may couple to the outer boomand may include a first side wall, a second side wall, a forward wall,and a rear wall. The forward wall and the rear wall both may include agenerally rectangular opening with a recess in each corner that allows afirst set of guide rails that are secured to the outer boom to passtherethrough. The outer surfaces of the forward wall and the rear wallmay be configured to contact edges of an outer boom upper wall, an outerboom first side wall, and an outer boom second side wall created by abreak along the length of each wall.

The forward stabilizer and the rear stabilizer both may include astabilizer upper wall, a stabilizer first side wall, and a stabilizersecond side wall. The stabilizer upper wall may be angled downward fromthe forward wall and configured to contact the outer boom upper wall.The stabilizer first side wall and the stabilizer second side wall maybe coupled to the edges of the stabilizer upper wall, angled inwardtherefrom, and configured to contact an upper portion of the first setof guide rails.

The roller bar may be coupled to the first side wall and the second sidewall, and may be configured to engage an upper portion of a second setof guide rails that are secured to the inner boom in order to relievethe pressure exerted on roller wheels attached to the inner boom whenthe inner boom is under load.

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the detaileddescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

Other aspects and advantages of the present invention will be apparentfrom the following detailed description of the embodiments and theaccompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

Embodiments of the present invention are described in detail below withreference to the attached drawing figures, wherein:

FIG. 1 is a perspective view of a telescopic boom apparatus comprisingan outer boom, an inner boom, and a mid roller assembly constructed inaccordance with various embodiments of the present invention;

FIG. 2 is a side view of the boom apparatus with the inner boom extendedand a portion of the outer boom cut away to display a first rollerassembly, a second roller assembly, and a third roller;

FIG. 3 is a side view of the boom apparatus with the inner boomretracted and a portion of the outer boom cut away similar to FIG. 2;

FIG. 4 is a sectional view of the boom apparatus taken along the line4-4 of FIG. 2, looking from a proximal end toward a distal end of theboom;

FIG. 5 is a sectional view of the boom apparatus taken along the line5-5 of FIG. 3, looking from the distal end toward the proximal end ofthe boom;

FIG. 6 is a perspective view of the proximal end of the inner boomshowing a sectional view of the first roller assembly;

FIG. 7 is a perspective view of the proximal end of the inner boomshowing a cut away view of a second set of guide rails;

FIG. 8 is a sectional view of the boom apparatus taken along the line5-5 of FIG. 3, looking from the proximal end toward the distal end ofthe boom;

FIG. 9 is a sectional view of an upper roller of the second rollerassembly;

FIG. 10 is a sectional view of a lower roller of the second rollerassembly;

FIG. 11 is a perspective view of a portion of the boom apparatus withthe mid roller assembly isolated from the outer boom;

FIG. 12 is a perspective view of the outer boom, with portions of theouter boom removed and portions of the second roller assembly and themid roller assembly hidden to display a first set of guide rails; and

FIG. 13 is a top view of a portion of the boom apparatus with interiorcomponents shown in dashed line.

The drawing figures do not limit the present invention to the specificembodiments disclosed and described herein. The drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following detailed description of the invention references theaccompanying drawings that illustrate specific embodiments in which theinvention can be practiced. The embodiments are intended to describeaspects of the invention in sufficient detail to enable those skilled inthe art to practice the invention. Other embodiments can be utilized andchanges can be made without departing from the scope of the presentinvention. The following detailed description is, therefore, not to betaken in a limiting sense. The scope of the present invention is definedonly by the appended claims, along with the full scope of equivalents towhich such claims are entitled.

In this description, references to “one embodiment”, “an embodiment”, or“embodiments” mean that the feature or features being referred to areincluded in at least one embodiment of the technology. Separatereferences to “one embodiment”, “an embodiment”, or “embodiments” inthis description do not necessarily refer to the same embodiment and arealso not mutually exclusive unless so stated and/or except as will bereadily apparent to those skilled in the art from the description. Forexample, a feature, structure, act, etc. described in one embodiment mayalso be included in other embodiments, but is not necessarily included.Thus, the present technology can include a variety of combinationsand/or integrations of the embodiments described herein.

A telescopic boom apparatus 10 that includes a mid roller assembly 11constructed in accordance with various embodiments of the presentinvention is shown in FIG. 1. The boom apparatus 10 is similar in manyrespects to the boom apparatus described in U.S. Pat. No. 5,515,654,issued May 14, 1996, and incorporated by reference herein in itsentirety.

The boom apparatus 10 broadly includes an elongated hollow outer boom12, an elongated inner boom 14 telescopically received within the outerboom 12, and a guidance structure 15 for guiding the inner boom 14 fortelescoping movement in and out of the outer boom 12.

In more detail, the outer boom 12 is formed of tubular steel andpresents a rectangular cross section. The outer boom 12 has opposedaxial distal and proximal ends 16 and 18 and a hollow passagewayextending therebetween. Attachment plates 20 are secured to the proximalend 18 of the outer boom 12 for coupling the outer boom 12 to a truck ora tractor. As those skilled in the art will appreciate, the truck ortractor is provided with conventional hydraulic cylinders or geardevices for telescopically extending or retracting the inner boom 14relative to the outer boom 12.

The inner boom 14 is telescopically received within the outer boom 12and is configured for axial telescopic movement about the longitudinalaxis of the outer boom 12 (see FIGS. 1-3). The inner boom 14 is formedof tubular steel and presents a rectangular cross section. The innerboom 14 has axially opposed distal and proximal ends 24 and 26. Thedistal end 24 has walls defining an opening for receiving a conventionaltool barrel 28. The tool barrel 28 has structure for coupling with anysuitable tool such as a scaling tool 30 or a scraper for dislodgingloose rock deposits from the ceiling of a mine. As those skilled in theart will appreciate, the proximal end 26 of the inner boom 14 is coupledto a hydraulic cylinder or gear device on the truck or tractor fortelescopically extending or retracting the inner boom 14 relative to theouter boom 12.

The guidance structure 15 is provided for telescopically guiding theinner boom 14 in and out of the outer boom 12. As best illustrated inFIGS. 2-5, the guidance structure 15 broadly includes a first set ofguide rails 22 attached to the interior corners of the outer boom 12, asecond set of guide rails 22 a secured to the inner boom 14, a firstroller assembly 32 attached to the proximal end 26 of the inner boom 14for engaging the guide rails 22, a second roller assembly 34 attached tothe distal end 16 of the outer boom 12 for engaging the guide rails 22 aduring telescopic movement, and the mid roller assembly 11 describedbelow.

The elongated guide rails 22 are attached to the interior corners of theouter boom 12 and extend the entire longitudinal length of the outerboom 12. The guide rails 22 are formed of elongated steel rods and eachpresents an arcuate wheel-engaging portion having a specific radius ofcurvature. In exemplary embodiments, the wheel-engaging portions of theguide rails 22 present a radius of approximately 1.25″.

The first roller assembly 32 is attached to the proximal end 26 of theinner boom 14 and is configured for engaging the guide rails 22 attachedto the outer boom 12. As illustrated in FIGS. 4 and 6-7, the firstroller assembly 32 includes a support frame 36 and a plurality of wheels38, 40, 42 and 44 rotatably mounted to the support frame 36. The supportframe 36 is welded or bolted to the proximal end 26 of the inner boom 14and is formed of steel. The support frame 36 presents a rectangularcross section having approximately the same dimensions as the crosssection of the inner boom 14. The support frame 36 includes four postmembers 46 extending parallel to the longitudinal axis of the inner boom14. Each post member 46 includes a slot therein for coupling with thewheels 38, 40, 42 and 44 as described below.

The wheels 38, 40, 42 and 44 are configured for engaging the guide rails22 positioned in the outer boom 12. The wheels 38, 40, 42 and 44 arerotatably mounted on axles 48 extending through the slots of the postmembers 46. Each of the wheels 38, 40, 42 and 44 includes an arcuaterail-engaging portion 50 for engaging the corresponding wheel-engagingportions of guide rails 22. The arcuate rail-engaging portion 50presents a radius of curvature approximately equal to the radius ofcurvature of the arcuate wheel-engaging portions of the guide rails 22.

The rail-engaging portions 50 of the wheels 38, 40, 42 and 44 present anexemplary radius of curvature of approximately 1.25″ which is identicalto the radius of curvature of the guide rails 22. With thisconfiguration, the arcuate rail-engaging portions 50 of the wheels 38,40, 42 and 44 engage a full quadrant of the surface area of the guiderails 22. Thus, the wheels 38, 40, 42 and 44 securely engage the guiderails 22 during axial telescopic movement of the inner boom 14.

As best illustrated in FIGS. 6 and 7, each of the wheels 38, 40, 42 and44 also includes a pair of generally annular lip portions 52 extendingtangentially from each end of the arcuate rail-engaging portions 50. Thelip portions 52 envelop a portion of the guide rails 22 for maintainingthe engagement between the wheels 38, 40, 42 and 44 and the guide rails22.

In various embodiments, the two uppermost wheels 38 and 40 of the firstroller assembly 32 are mounted on axles 48 having eccentric axes. Theaxis of the eccentric axle 48 is slightly displaced from the geometriccenter of the axle 48. When the eccentric axle 48 is rotated, theposition of the arcuate rail-engaging portion 50 is shifted relative tothe arcuate wheel-engaging portions of the guide rails 22. This allowsthe uppermost wheels 38 and 40 of the first roller assembly 32 to beadjusted to properly align the guidance structure 15. For example, ifthe rail-engaging portions 50 of the uppermost wheels 38 and 40 do notsecurely engage the wheel-engaging portions of the guide rails 22, theeccentric axles 48 of the two uppermost wheels 38 and 40 can be rotatedto reposition the uppermost wheels 38 and 40 closer to the guide rails22. Alternatively, if the uppermost wheels 38 and 40 are spaced too farapart from the lowermost wheels 42 and 44 to fit within the guide rails22, the axles 48 of the two uppermost wheels 38 and 40 can be rotatedthe opposite direction to reposition the uppermost wheels 38 and 40.

In various embodiments, the wheels 38, 40, 42 and 44 are not attached tothe axles 48 with fasteners or bolts, but are freely mounted thereto.Once the wheels 38, 40, 42 and 44 engage the guide rails, they aresecured to the axles 48 by the guide rails 22. With this configuration,the wheels can be easily replaced and/or repaired by disengaging themfrom the guide rails 22 and simply removing them from the axles 48.

As best illustrated in FIG. 5, the second roller assembly 34 includes asupport frame 54 attached to the distal end 16 of the outer boom 12 andpair of roller bars 56 and 58 rotatably mounted thereto. The roller bars56 and 58 are configured for engaging the outer surface of the innerboom 14 during telescopic movement. As seen in FIG. 5, the roller bars56 and 58 engage guide rails 22 a secured to or integrally formed withthe outer surface of the inner boom 14.

The support frame 54 includes a pair of elongated steel plates 60extending vertically relative to the longitudinal axis of the outer boom12. The steel plates 60 are attached to opposed sides of the distal end16 of the outer boom 12 and include a plurality of slots 62 therein.

As best illustrated in FIGS. 9 and 10, the roller bars 56 and 58 arerotatably mounted on a pair of shafts 64 and 66 extending through theslots 62 in the steel plates 60. A pair of conventional lockingfasteners 68, such as the trantorque device manufactured by FennerManheim, are fastened to the ends of the shafts 64 and 66 for retainingthe roller bars 56 and 58 on the shafts 64 and 66.

Each roller bar 56 and 58 includes a pair of axially opposed flangemembers 70 positioned on the ends of each of the shafts 64 and 66 forengaging the corners of the inner boom 14. Each of the flanges 70includes an arcuate portion 72 for engaging the outside corners of theinner boom 14. The flanges 70 also include a generally annular lipportion 74 extending tangentially from the arcuate portion 72 formaintaining the engagement between the flange members 70 and the outsidecorners of the inner boom 14.

In various embodiments, the uppermost roller bar 56 is rotatably mountedabout a shaft having an eccentric axis. The axis of the eccentric shaft64 is slightly displaced from the geometric center of the shaft 64. Withthis configuration, the uppermost roller bar 56 can be repositionedabout a vertical axis relative to the inner boom 14 by rotating theeccentric shaft 64.

The mid roller assembly 11, best seen in FIG. 11 and also shown in FIGS.8 and 12-13, comprises a housing 76, a forward stabilizer 78, a rearstabilizer 80, and a third roller bar 82. The mid roller assembly 11 isgenerally positioned along the outer boom 12 a distance from the secondroller assembly 34 and in the direction of the proximal end 26 of theinner boom 14.

The housing 76 may include a forward wall 84, a rear wall 86, a housingfirst side wall 88, a housing second side wall 90, a plurality ofgussets 92, and a cover plate 94. The forward wall 84 and the rear wall86 are spaced apart from one another with the housing first side wall 88and the housing second side wall 90, also spaced apart, positionedorthogonally therebetween. The forward wall 84 may be positioned towardthe distal end 24 of the inner boom 14, and the rear wall 86 may bepositioned toward the proximal end 26.

The forward wall 84 and the rear wall 86 may be substantially similar toone another, and both may include a generally rectangular boom opening96, whose inner perimeter is shaped to match the cross-sectional shapeof the outer boom 12. The corners of each boom opening 96 may include anarcuate rail-engaging recess 98 that contact the outer perimeter of theguide rails 22 of the outer boom 12. Between the forward wall 84 and therear wall 86, the upper guide rails 22 may have a rail separation orrail break 100, seen in FIGS. 11 and 13, along their length toaccommodate the third roller bar 82. In addition, outer boom upper wall102, outer boom first side wall 104, and outer boom second side wall 106each include a wall break 108 along their length, seen in FIGS. 11-13.The edges of the outer boom upper wall 102, the outer boom first sidewall 104, and the outer boom second side wall 106 created by the wallbreak 108 contact the outer surfaces of the forward wall 84 and the rearwall 86 of the housing 76. An outer boom lower wall 110 generally doesnot include a break, and the perimeter of the boom opening 96 of theforward wall 84 and the rear wall 86 contacts the outer surface of theouter boom lower wall 110. The boom opening 96 may be further positionedsuch that the inner boom 14 passes through the boom opening 96 of boththe forward wall 84 and the rear wall 86 of the housing 76.

The housing first side wall 88 and the housing second side wall 90 maybe positioned inward from the edges of the forward wall 84 and the rearwall 86. The gussets 92 may be positioned extending lengthwise betweenthe forward wall 84 and the rear wall 86 in the space between thehousing first and second side walls 88, 90 and the edges of the forwardwall 84 and the rear wall 86. The gussets 92 may also be evenly spacedalong the length of the housing first and second side walls 88, 90 andgenerally add structural strength between the forward wall 84 and therear wall 86.

The cover plate 94 may be positioned on the upper edges of the forwardwall 84 and the rear wall 86, and may be aligned with or parallel to theouter boom upper wall 102. The cover plate 94 offers a top cover to themid roller assembly 11 and may be removed to access the third roller bar82.

The forward stabilizer 78 and the rear stabilizer 80 are substantiallysimilar to one another and both include a stabilizer upper wall 112, astabilizer first side wall 114, and a stabilizer second side wall 116.The forward stabilizer 78 extends outward from the outer surface of theforward wall 84, and the rear stabilizer 80 extends outward from theouter surface of the rear wall 86. The forward stabilizer upper wall 112may be positioned at a downward angle from the forward wall 84 and maycontact the outer boom upper wall 102. The top edge of the forwardstabilizer upper wall 112 may be wider than the width of the outer boomupper wall 102. The forward stabilizer first side wall 114 and theforward stabilizer second side wall 116 may couple to the side edges ofthe forward stabilizer upper wall 112 and extend inward to contact thetop surface of the upper guide rails 22. The upper wall 112, the firstside wall 114, and the second side wall 116 of the rear stabilizer 80may have the same configuration as the forward stabilizer 78 withrespect to the rear wall 86 and the outer boom upper wall 102, as shownin FIG. 13. The forward stabilizer 78 and the rear stabilizer 80generally stabilize the mid roller assembly 11 as the inner boom 14extends and retracts within the outer boom 12.

The third roller bar 82 may be substantially similar to the uppermostroller bar 56 and may include the axially-opposed flange members 70 witharcuate portions 72 and annular lip portion 74, as shown in FIG. 8. Thethird roller bar 82 may further be mounted on an eccentric mid rollershaft 118 that is substantially similar to eccentric shaft 66. The endsof the mid roller shaft 118 may be coupled to the housing first sidewall 88 and the housing second side wall 90 using the fasteners 68. Asshown in FIG. 8, the flange members 70 of the third roller bar 82 mayengage the upper set of the second guide rails 22 a in the same fashionas the flanges 70 on upper roller bar 56. The third roller bar 82rotates as the inner boom 14 moves in and out. In addition, the heightof the third roller bar 82 with respect to the inner boom 14 may beadjusted by rotating the eccentric mid roller shaft 118 in a similarfashion to the shaft 66.

In operation, the guidance structure 15 of the above described boomapparatus 10 effectively maintains the telescopic engagement between theinner boom 14 and the outer boom 12 during axial telescopic movement.The boom apparatus 10 is shown in FIG. 2 with the inner boom 14extended, and in FIG. 3 with the inner boom 14 retracted. The wheels 38,40, 42 and 44 of the first roller assembly 32 engage the guide rails 22for guiding the proximal end 26 of the inner boom 14 along the axiallength of the outer boom 12. The roller bars 56 and 58 of the secondroller assembly 34 as well as the third roller bar 82 engage the outersurface of the distal end 24 of the inner boom 14 for guiding the innerboom 14 in and out of the outer boom 12. The third roller bar 82provides relief of the pressure exerted on the upper wheels 38, 40 whenthe tool 30 is engaged and the distal end 24 of the inner boom 14 has aload on it.

If the guidance structure 15 of the boom apparatus 10 must be adjustedduring operation, the uppermost wheels 38 and 40 of the first rollerassembly 32 and the uppermost roller bar 56 of the second rollerassembly 34 can be rotated about their eccentric axes to reposition theguidance structure 15 relative to the outer and inner booms 12, 14.

Although the invention has been described with reference to theembodiments illustrated in the attached drawing figures, it is notedthat equivalents may be employed and substitutions made herein withoutdeparting from the scope of the invention as recited in the claims.

1. A roller assembly for use with a telescopic boom apparatus includingan extensible inner boom and an outer boom, the roller assemblycomprising: a housing coupled to the outer boom, the housing allowing afirst set of guide rails that are secured to the outer boom to passtherethrough; and a roller bar coupled to the first side wall and thesecond side wall, the roller bar configured to engage an upper portionof a second set of guide rails that are secured to the inner boom and torelieve the pressure exerted on roller wheels attached to the inner boomwhen the inner boom is under load.
 2. The roller assembly of claim 1,wherein the housing further includes a first side wall, a second sidewall, a forward wall, and a rear wall, wherein the forward wall and therear wall both include a generally rectangular opening with a recess ineach corner that allow the first set of guide rails to pass therethough.3. The roller assembly of claim 2, further including a forwardstabilizer coupled to the forward wall and a rear stabilizer coupled tothe rear wall, wherein the forward stabilizer and the rear stabilizerare both configured to contact an upper wall of the outer boom tostabilize the roller assembly during extension of the inner boom.
 4. Theroller assembly of claim 3, wherein the forward stabilizer and the rearstabilizer both include a stabilizer upper wall, a stabilizer first sidewall, and a stabilizer second side wall, the stabilizer upper wall beingangled downward from the forward wall and configured to contact theouter boom upper wall, the stabilizer first side wall and the stabilizersecond side wall coupled to the edges of the stabilizer upper wall,angled inward therefrom, and configured to contact an upper portion ofthe first set of guide rails.
 5. The roller assembly of claim 2, whereinouter surfaces of the forward wall and the rear wall are configured tocontact edges of an outer boom upper wall, an outer boom first sidewall, and an outer boom second side wall created by a break along thelength of each wall.
 6. The roller assembly of claim 2, wherein theopening of the forward wall and the rear wall are configured to allow anouter boom lower wall to pass therethrough continuously.
 7. The rollerassembly of claim 2, wherein the housing further includes a plurality ofgussets, each gusset extending longitudinally between the forward walland the rear wall, the gussets being positioned adjacent to the firstside wall and the second side wall inward from outer edges of theforward wall and the rear wall.
 8. The roller assembly of claim 2,wherein the housing further includes a cover plate removably coupled tothe forward wall, the rear wall, the first side wall, and the secondside wall, the cover plate being removed to access the roller bar. 9.The roller assembly of claim 2, further including an eccentric shaftcoupled to the first side wall and the second side wall and on which theroller bar is mounted, the eccentric shaft being rotatable to adjust theheight of the roller bar with respect to the inner boom.
 10. Atelescopic boom apparatus comprising: a elongated outer boom presentingopposed proximal and distal ends and a hollow passageway extendingtherebetween, the distal end presenting a cross sectional width; anextensible inner boom telescopically received within the outer boom foraxial telescoping movement in and out of the distal end of the outerboom, the inner boom having opposed proximal and distal ends; and aguidance structure for guiding the inner boom for axial telescopingmovement in and out of the distal end of the outer boom, the guidancestructure including: a first set of elongated guide rails secured withinthe outer boom passageway and extending parallel to the longitudinalaxis of the outer boom, each of the first set guide rails presenting anarcuate track surface, a plurality of roller wheels spacedcircumferentially about the proximal end of the inner boom, each of theroller wheels including an arcuate rail engaging surface for engagingthe track surfaces of the first set of guide rails during telescopingmovement of the inner boom, a second set of elongated guide railssecured to the inner boom, a pair of roller bars secured to the distalend of the outer boom for engaging the second set of guide rails forguiding the inner boom during axial telescoping movement in and out ofthe distal end of the outer boom, the roller bars being positioned onopposed sides of the distal end of the outer boom and extending acrosssubstantially the entire cross sectional width of the distal end of theouter boom, and a roller assembly including: a housing coupled to theouter boom, the housing including a first side wall, a second side wall,a forward wall, and a rear wall, wherein the forward wall and the rearwall both include a generally rectangular opening with a recess in eachcorner that allows the first set of guide rails to pass therethrough,and a third roller bar coupled to the first side wall and the secondside wall, the third roller bar configured to engage an upper portion ofthe second set of guide rails and to relieve the pressure exerted on anupper set of the roller wheels attached to the inner boom when the innerboom is under load.
 11. The boom apparatus of claim 10, at least one ofthe roller bars including an elongated shaft having an eccentric axisfor permitting adjustment of the position of the roller bars foraligning the roller bars with the inner boom.
 12. The boom apparatus ofclaim 10, the roller wheels each including an axle presenting aneccentric axis for permitting adjustment of the engagement of the rollerwheels on the first set of guide rails.
 13. The roller assembly of claim10, further including a forward stabilizer coupled to the forward walland a rear stabilizer coupled to the rear wall, wherein the forwardstabilizer and the rear stabilizer both contact an upper wall of theouter boom to stabilize the roller assembly during extension of theinner boom.
 14. The roller assembly of claim 13, wherein the forwardstabilizer and the rear stabilizer both include a stabilizer upper wall,a stabilizer first side wall, and a stabilizer second side wall, thestabilizer upper wall being angled downward from the forward wall andcontacting the outer boom upper wall, the stabilizer first side wall andthe stabilizer second side wall coupled to the edges of the stabilizerupper wall, angled inward therefrom, and contacting an upper portion ofthe first set of guide rails.
 15. The roller assembly of claim 10,wherein outer surfaces of the forward wall and the rear wall contactedges of an outer boom upper wall, an outer boom first side wall, and anouter boom second side wall created by a break along the length of eachwall.
 16. The roller assembly of claim 10, wherein the opening of theforward wall and the rear wall allow an outer boom lower wall to passtherethrough continuously.
 17. The roller assembly of claim 10, whereinthe housing further includes a plurality of gussets, each gussetextending longitudinally between the forward wall and the rear wall, thegussets being positioned adjacent to the first side wall and the secondside wall inward from outer edges of the forward wall and the rear wall.18. The roller assembly of claim 10, wherein the housing furtherincludes a cover plate removably coupled to the forward wall, the rearwall, the first side wall, and the second side wall, the cover platebeing removed to access the third roller bar.
 19. The roller assembly ofclaim 10, further including an eccentric shaft coupled to the first sidewall and the second side wall and on which the third roller bar ismounted, the eccentric shaft being rotatable to adjust the height of thethird roller bar with respect to the inner boom.